The Partition Table field shows that I am using a msdos MBR partition table (the one still commonly used for Linux and Windows) on both disks. From the man page parted can create (and thus hopefully identify) the following types of partition table (or more broadly `disk label'):

bsd
dvh
gpt - this is a GPT partition table
loop - this is raw disk access without a partition table
mac
msdos - this is a standard MBR partition table
pc98
sun

Update

It is worth adding the command for listing a single partition since this is not obvious without some knowledge of parted and it can be a pain finding the data you need if there are multiple drives. For /dev/sda you would do:

If you don't see this warning, you have a GPT disk, or a hybrid GPT/MBR disk. The later are used mostly on Apple machines intended to dual-boot versions of MS Windows which do not support GPT. gdisk will indicate this with:

Found valid GPT with hybrid MBR; using GPT

They may also be used in other situations where support for both styles is required.

Or the reverse - trying to use cfdisk on a GPT partition will also result in a warning.
– orionMar 18 '14 at 14:54

If not installed and not in a gdisk package, it can be found in the gptfdisk package... at least on Gentoo.
– jus cogens primeMar 18 '14 at 15:22

2

@orion I would not recommend that as some versions of tools like fdisk or cfdisk may support GPT and therefore not show an error.
– goldilocksMar 18 '14 at 15:37

For me gdisk detects a hybrid GPT+MBR partition table and gives Found valid GPT with hybrid MBR; using GPT.. This seems to be the only method which will detect a hybrid table.
– GraemeMar 18 '14 at 19:11

@Graeme : Thanks. I was unaware of these (the original hybrid reference was edited in by Stephane Chazelas), but I did a bit of reading and added some details.
– goldilocksMar 18 '14 at 20:34

Note that you will get similar output regardless of whether there is a hybrid GPT+MBR or not. GPT requires a fake MBR with a single full disk partition of type 0xee. In a hybrid this is a normal MBR with one 0xee partition (and potential for major problems if the MBR data goes out of sync with the GPT data).
– GraemeMar 18 '14 at 18:55